DESCRIPTION

In FreeBSD 8.0, the kthread*(9) family of functions was renamed to be the
kproc*(9) family of functions, as they were misnamed and actually
produced kernel processes. A new family of differentkthread_*(9)
functions was added to produce real kernel threads. See the kthread(9)
man page for more information on those calls. Also note that the
kproc_kthread_add(9) function appears in both pages as its functionality
is split.
The function kproc_start() is used to start ``internal'' daemons such as
bufdaemon, pagedaemon, vmdaemon, and the syncer and is intended to be
called from SYSINIT(9). The udata argument is actually a pointer to a
structkproc_desc which describes the kernel process that should be
created:
struct kproc_desc {
char *arg0;
void (*func)(void);
struct proc **global_procpp;
};
The structure members are used by kproc_start() as follows:
arg0 String to be used for the name of the process. This
string will be copied into the p_comm member of the
new process' structproc.
func The main function for this kernel process to run.
global_procpp A pointer to a structproc pointer that should be
updated to point to the newly created process'
process structure. If this variable is NULL, then
it is ignored.
The kproc_create() function is used to create a kernel process. The new
process shares its address space with process 0, the swapper process, and
runs in kernel mode only. The func argument specifies the function that
the process should execute. The arg argument is an arbitrary pointer
that is passed in as the only argument to func when it is called by the
new process. The newpp pointer points to a structproc pointer that is
to be updated to point to the newly created process. If this argument is
NULL, then it is ignored. The flags argument specifies a set of flags as
described in rfork(2). The pages argument specifies the size of the new
kernel process's stack in pages. If 0 is used, the default kernel stack
size is allocated. The rest of the arguments form a printf(9) argument
list that is used to build the name of the new process and is stored in
the p_comm member of the new process's structproc.
The kproc_exit() function is used to terminate kernel processes. It
should be called by the main function of the kernel process rather than
letting the main function return to its caller. The ecode argument
specifies the exit status of the process. While exiting, the function
exit1(9) will initiate a call to wakeup(9) on the process handle.
The kproc_resume(), kproc_suspend(), and kproc_suspend_check() functions
are used to suspend and resume a kernel process. During the main loop of
its execution, a kernel process that wishes to allow itself to be
suspended should call kproc_suspend_check() passing in curproc as the
only argument. This function checks to see if the kernel process has
been asked to suspend. If it has, it will tsleep(9) until it is told to
resume. Once it has been told to resume it will return allowing
execution of the kernel process to continue. The other two functions are
used to notify a kernel process of a suspend or resume request. The p
argument points to the structproc of the kernel process to suspend or
resume. For kproc_suspend(), the timo argument specifies a timeout to
wait for the kernel process to acknowledge the suspend request and
suspend itself.
The kproc_shutdown() function is meant to be registered as a shutdown
event for kernel processes that need to be suspended voluntarily during
system shutdown so as not to interfere with system shutdown activities.
The actual suspension of the kernel process is done with kproc_suspend().
The kproc_kthread_add() function is much like the kproc_create() function
above except that if the kproc already exists, then only a new thread
(see kthread(9)) is created on the existing process. The func argument
specifies the function that the process should execute. The arg argument
is an arbitrary pointer that is passed in as the only argument to func
when it is called by the new process. The procptr pointer points to a
structproc pointer that is the location to be updated with the new proc
pointer if a new process is created, or if not NULL, must contain the
process pointer for the already exisiting process. If this argument
points to NULL, then a new process is created and the field updated. If
not NULL, the tdptr pointer points to a structthread pointer that is
the location to be updated with the new thread pointer. The flags
argument specifies a set of flags as described in rfork(2). The pages
argument specifies the size of the new kernel thread's stack in pages.
If 0 is used, the default kernel stack size is allocated. The procname
argument is the name the new process should be given if it needs to be
created. It is NOT a printf style format specifier but a simple string.
The rest of the arguments form a printf(9) argument list that is used to
build the name of the new thread and is stored in the td_name member of
the new thread's structthread.

RETURNVALUES

The kproc_create(), kproc_resume(), and kproc_suspend() functions return
zero on success and non-zero on failure.

ERRORS

The kproc_resume() and kproc_suspend() functions will fail if:
[EINVAL] The p argument does not reference a kernel process.
The kproc_create() function will fail if:
[EAGAIN] The system-imposed limit on the total number of
processes under execution would be exceeded. The
limit is given by the sysctl(3) MIB variable
KERN_MAXPROC.
[EINVAL] The RFCFDG flag was specified in the flags parameter.

SEEALSO

HISTORY

The kproc_start() function first appeared in FreeBSD 2.2. The
kproc_shutdown(), kproc_create(), kproc_exit(), kproc_resume(),
kproc_suspend(), and kproc_suspend_check() functions were introduced in
FreeBSD 4.0. Prior to FreeBSD 5.0, the kproc_shutdown(), kproc_resume(),
kproc_suspend(), and kproc_suspend_check() functions were named
shutdown_kproc(), resume_kproc(), shutdown_kproc(), and
kproc_suspend_loop(), respectively. Originally they had the names
kthread_*() but were changed to kproc_*() when real kthreads became
available.